The present invention relates to electronic switches and more particularly to electronic switches using Field Effect Transistors (FETs) suitable for use in integrated circuits as analog switch devices or transmission gates.
Any electronic switch employing FETs exhibits capacitive coupling of the switching signal applied at the FET gate to the switch output and input, FET source and drain, respectively. This cause voltage "spikes" to appear in the switched signal. The problem is especially troublesome when the switch is used, for example, in a sample-and-hold configuration because the spikes can be remembered by the holding circuit. Present methods for reducing these spikes use matched size N-channel and P-channel FETs in parallel, with the gates driven by opposite polarity signals as shown in FIG. 1. This causes coupling from a rising switch signal on the N-channel gate, for example, to be partially cancelled by coupling from a falling signal on the P-channel gate. A major problem with this approach is that the two gate signals of opposite polarity can never be generated at precisely the same time. Because of the skew between the opposite polarity signals the output experiences, for example, an "up" spike followed by a "down" spike.
It is an object of the present invention to provide an electronic switch which reduces spikes from switching noise.